1. Field of the Invention
The present invention relates to an electronic component mounting board used for a high-frequency portion of a radio communication apparatus, for example, a transmission module for a radio communication apparatus, and an electronic component module using the board.
2. Related Art of the Invention
In recent years, a number of antenna switch duplexer modules and power amplifier modules are used for the high-frequency part of a radio communication apparatus. Referring to the accompanying drawings, the following discusses conventional individual modules and an example of a high-frequency portion of a radio communication apparatus which combines the modules.
FIG. 5 is a block diagram showing an antenna switch duplexer module and a power amplifier module in a conventional radio communication apparatus. In FIG. 5, reference numeral 406 denotes an antenna switch duplexer module, reference numeral 404 denotes a power amplifier module, reference numeral 405 denotes an isolator module, and reference numeral 407 denotes a filter for reception.
The antenna switch duplexer module 406 is may use a PIN diode and a compound semiconductor IC of GaAs. The power amplifier module 404 may use a compound semiconductor IC such as GaAs and InGaP. Individually corresponding components are used for the filter for reception 407 and the isolator module 405. These modules and the separate components are arranged on a printed board and are electrically connected via wiring such as a microstrip line.
However, since the above configuration uses separate modules and components, the miniaturization of the radio communication apparatus is limited and it is difficult to reduce the cost in the separate configurations. Further, since the connection is made by wiring on the printed board, impedance is disturbed at a high frequency, desired characteristics cannot be reproduced, and an adjustment step is necessary. Furthermore, the wiring on the printed board causes excessive loss and requires higher power consumption.
In order to solve these problems, as shown in a top view of FIG. 6(a) and a side sectional view of FIG. 6(b), a radio communication module has been proposed in which separate modules such as an antenna switch 601, a power amplifier 602, and a VCO 603, and semiconductor components are flip-chip mounted on a thick-film multilayer board 600 including passive elements 604 (e.g., Japanese Patent Laid-Open No. 2002-261643). The disclosure of Japanese Patent Laid-Open No. 2002-261643 is incorporated herein by reference in its entirety.
However, in the above-described radio communication module, heat has been is released from a component such as the power amplifier 602 which generates a large amount of heat. Particularly when a ceramic multilayer board is used as a thick-film multilayer board, the problem of heat release cannot be ignored.
As shown in FIG. 6(b), via holes 605 making electrical connection are used to release heat from components mounted on a board. However, the use of vias causes a problem described below.
The vias 605 are formed concurrently with the board by filling a metal such as aluminum having conductivity or a thermal conductivity into via holes, which are provided so as to penetrate a green sheet serving as a base of the board, and baking the green sheet thereafter.
While ceramic shrinks during baking, metal thermally expands by the heat of baking. Therefore, as the via hole becomes smaller in diameter, the metal increases in diameter. Thus, when the diameter of the via hole is too small, cracks appear on the via hole due to the expanded metal, resulting in a lower yield during manufacturing.
Meanwhile, when the diameter of the via hole is too large, a gap appears between the metal shrunk after completion of baking and the via hole, resulting in low efficiency of heat release.